A range of extracted plant derived hydrocolloids are traditionally used as texturizing agents for various food products. However, many food products, such as fruits and vegetables in themselves contain hydrocolloids, i.e. the plant cell wall material. With the aim of improving, in situ, viscosity and gelling capacity, a further enzymatic modification of the plant cell wall material per se is now proposed as a texturizing process.
The plant cell wall has a very complex nature consisting of different polysaccharides, small amounts of glycoproteins and phenolic compounds. The polysaccharides are traditionally divided into cellulose compounds, hemicellulose and pectic compounds.
The primary cell wall of most flowering plants are of the type I cell wall. In a type I cell wall the cellulose microfibrils are interlaced with xyloglucan polymers (approx. 50% of the total mass). The cellulose-xyloglucan framework is embedded in a matrix of pectic polysaccharides. The pectic matrix consists of smooth regions of polygalacturonic acids and of rhamnogalacturonan. The polygalacturonic acid areas are usually highly esterified by methoxyl groups, acetylation of the hydroxy groups also occurs. Side groups consisting of araban, galactan and arabinogalactan are attached to the rhamnogalacturonan residues. The pectic polysaccharides constitute approx. 30.degree. C. of the total mass. Mannans, .beta.-(1-3)-glucans and arabinoxylans also play a role as pectic-interlocking agents. The cell wall further consists of structural proteins, of which extensin is thought to play the major role. (Carpita, N. C. and Gibeaut, D. M., 1993, Plant Journal 3 (1), 1-30, Keegstra, K. et al, 1973, Plant Physiol., 51, 188-196).
The endogenous, highly methoxylated content of pectin (HM pectin) in various fruits and vegetables can enzymatically be modified to a low methoxylated pectin (LM pectin) by pectinesterase (PE)(EC 3.1.1.11). In combination with the natural content or further addition of calcium ions this is sufficient for an in situ gelation or an in situ thickening to take place (Calesnik, E. J. et al 1950, Arch. of Biochem., 29, 432-440. Meurens, M., 1978, Rev. Ferment. Ind. Aliment., 33, 95-104). These authors also indicate that use of a PE preparation purified is for pectic depolymerizing enzymes, such as polygalacturonases, would allow the gelation to take place by utilising the endogenous pectin in situ.
Such a process is furthermore described in International patent application no. PCT/EP93/03379 (Gist-Brocades NV), where also the use of a PE substantially free from pectic depolymerizing enzymes is described for the gelling of food products.
However, these methods still leave room for improving the properties of such food products.
It is thus the object of this invention to provide a method for increasing the viscosity or gel strength in a pectinaceous mass.